Recently, much progress has been made in increasing the brightness of light emitting diodes (LEDs). As a result, LEDs have become sufficiently bright and inexpensive, to serve as a light source in for example illumination arrangements such as lamps with adjustable color. By mixing differently colored LEDs any number of colors can be generated, e.g. white. An adjustable color lighting system is typically constructed by using a number of primary colors, and in one example, the three primaries red, green and blue are used. The color of the generated light is determined by the LEDs that are used, as well as by the mixing ratios. To generate “white”, all three LEDs have to be turned on.
By using LEDs it is possible to decrease the energy consumption, a requirement, which is well in line with the current environmental trend. For further decreasing the energy consumption of the illumination arrangement it is possible to include light sensors and presence detectors, which will detect changes in ambient lighting and approaching persons, respectively. Such additions may in turn lead to a decrease in the time the illumination arrangement is active, as well as an intensity decrease by taking into account the ambient lighting.
An example of such a lighting system is disclosed in US 2009/0310348 A1, where a plurality of spaced apart light sources are provided for illuminating a space, each of the light sources having plural solid-state lighting devices, as well as means for sensing movement of people in the space relative to locations of the light sources. In a first case where people are detected, there is provided light having a set illumination level and being of “good quality”, i.e. having a relatively high CRI. Conversely, in a second case where people are not detected, light having the same set illumination level is provided but instead of “bad quality”, i.e. having a relatively low CRI. By means of such a lighting system it is possible to keep a set illumination level within the space even when no people are present as well as optimizing the efficiency of light emitted by the system. This is made possible since generally light having a relatively low CRI is more energy efficient than light having a relatively high CRI.
However, even though US 2009/0310348 A1 at least in some sense decrease the energy consumption of the lighting system, in this case by making use of detection of people in the space, it may be desirable to provide further enhancements to be able to even further decrease the energy consumption within the space.